Lecture 10: Chemical Evolution of Galaxies. Metalicity evolution Z(t) vs galaxy type : Processes that alter the metalicity: Type-II SNe enrich the ISM. Low-mass stars form from enriched ISM and “lock-up” metals. 3. Primordial gas falls in from IGM.
M0 = total mass
MG(t) = mass of gas in ISM
MZ(t) = mass of metals in ISM
MS(t) = mass of the long-lived stars
that lock up metals
Integrate (with r = constant ) :
At Z = 0, MG = M0 :
The equation above is valid when Z < r, after which Z = r.
First generation: Z=0 later generations Z << ZSN :
From Salpeter IMF and SN 1987A: a = 0.93
From SN 1987A: ZSN = 0.13
However, note that which is larger than the calculated yield, implying ! (remember )